1. Field of the Invention
This disclosure generally relates to automatic data collection (ADC) and more particularly to radio-frequency identification.
2. Description of the Related Art
The ADC field is generally directed to the use of devices and methods for automatically capturing data typically encoded in media such as a machine-readable symbol or tag carried by the item to which the data relates. A variety of ADC devices and ADC media are ubiquitous and well known.
For example, a data carrier may take the form of a radio-frequency identification (RFID) tag, which may take the form of a card. Such tags typically include an RFID substrate carrying a circuitry such as a semiconductor device including memory and one or more conductive traces that form an antenna. Typically, RFID tags act as transponders, providing information stored in the semiconductor device in response to a radio-frequency (RF) signal, commonly referred to as an interrogation signal, received at the antenna from a reader or interrogator. Some RFID tags include security measures, such as passwords and/or encryption. Many RFID tags also permit information to be written or stored in the semiconductor memory via an RF signal.
RFID tags that include a discrete power source, for example a battery, are commonly referred to as active devices. RFID devices that rely on an RF signal to derive power are commonly referred to as passive devices. RFID tags may employ both active and passive power sources.
Identification of an RFID device or tag generally depends on RF energy produced by a reader or interrogator arriving at the RFID tag and returning to the interrogator. In general, lower frequencies can penetrate objects better than higher frequencies, but higher frequencies can carry more data than lower frequencies. In addition, multiple protocols exist for use with RFID tags. These protocols may specify, among other things, particular frequencies, frequency ranges, modulation schemes, security schemes, and data formats. Conventional approaches employ multiple RFID tags, each tag using a frequency band and protocol suited to a particular application.